Metered piston truss



Feb. 19, 1935. 2-. A. BRUEGGER METERED PISTON TRUSS Filed April 12, 1935 1 m R M O R M.

- A 1 I /6 g WITNESSES a, 75/41/1022 Patented Feb. 19, 1935 1,991,655

UNITED STATES PATENT OFFICE METERED rIs'roN muss Zeno Arno Brnegger, Boise, Idaho Application April 12, 1933, Serial No. tesszs 9 Claims. (01. 309-12) This invention relates to improvements in pistrating one style of truss as an integral part of tons, and its objects are as follows: the piston instead of a separate resilient body. First, to provide a truss or brace for a piston, Figure '7 is a sectional view of a part of a mold enerally an aluminium or aluminium alloy pisillustrating that step in the method of casting ton, which is automatically made to perform its wherein the truss in Figure 6 is produced with a 5 function when the piston has expanded to the metered space by an inserted shim oi. the correct limit in the region of its skirt, said truss, which thickness. has parts normally spaced, approximately com- The instant invention is a development of the ing together when said limit of expansion is principle disclosed in U. S. Patent 1,911,103 of 10 reached thereby to reinforce the skirt and make May 23, 1933, for Metered-kerf piston to Zeno 10 the piston virtually a solid member even though Arno Bruegger. it has one or more of the numerous types of ex- That principle is to provide for the approxipansion slots. mate closure at certain places of the customarily Second, to provide a spring ring or other anover-sized expansion slots inapiston under Worknulus either inherently separate from the piston ing conditions so that the piston is converted 15 and insertable therein, or made as an originally virtually into a solid member, proof against the integral part of the piston, being combined with collapse of the head under the crushing force of the slotted skirt and having a split metered to compression while the piston is between the trethe known amount of over-expansion of the mendous power impulses and the crank shaft load piston so that the ends of the annulus will apresistance. 1 proximately abut at maximum piston expansion It is now contemplated to guard the pistonthus producing a solid support for the erstwhile skirt from collapse by introducing therein a mecrushable piston and preventing skirt collapse. tered annulus, truss or brace. It is not always Third, to provide a variety of modes of meternecessary to adhere to an annulus to form the ing the split in the annulus in the event of its metered truss or brace. Any other form of truss- 25 being a spring ring or equivalent spring body. ing will give the sanle results when metered in Fourth, to provide a spring ring having ends any available manner. The type of piston in which will approximately abut at maximum pismind is that which has expansion relief slots in ton expansion. its skirt. These slots are necessary to make room Fifth, to inserts. metered shim in the core as for the expansion of the skirt under working 30 the important method step oi! casting the anconditions. Without any known exception these nulus, brace or truss integral with the piston. slots are always over-sized, that is to say, they Other objects and advantages will appear in are wider than actually necessary to make room the following specification, .reference being had for the maximum expansion of the skirt. Thereto the accompanying drawing in which. fore, there is always enough residual slot room 35 Fi ure 1 is a detail Vi w la Pi n firt fll to enable the opposite sides of the skirt to yield trating how a known type of expanding r 8 18 when they are pressed against the cylinder walls equipped with attached pads the spacing which during the inward and outward strokes of the is meteredto the proportionate amount of overpiston expansion the 13mm This sets up a rocking motion of the piston on I igure 2 is detail view or the its wrist pin. That rocking motion is commonly ing the use of a set screw for producing the metered moa identified as piston slap. Piston slap occurs be pigmring cause the piston does not contact against the the g g fi i fi gggfi gi ggg cylinder walls, and it increases in intensity dur- 45 purpose. ing continued operation because the skirt temper Figure 4 is a det i i of t ring showing fatigues allowing the skirt to collapse with the result that it becomes tapered more and more. 3313 20??? oi' th fi n formed m informing It stands to reason that the older the piston Figure 5 is a cross section of a piston n; becomes the lower will its resistance become to so taken immediately above the wrist pin bosses w r l p 91 th kir under the vy and showing how another type of expander is forces by which it is, driven against the opposite equipped with means for providing it with a. cylinder walls. There are on the market devices metered space. known as expanders which are fitted into the ma- Figuredisaverticalsectionotapistonillustonskirt anddesigned topress it outwardlyin 66 an attempt to of the cylinder.

One type of the expander is disclosed in the patent to H. F. Phillips, 1,806,416, May 19, 1931. This expander is in the general form of a ring. It is held in the piston when inserted, and by virtue of its resilience an outward pressure is imposed on the skirt so as to repeatedly force the skirt back yieldingly against the cylinder wall.

There is also another type of piston expander on the market in the nature of a resilient body which is adapted to press against the wrist pin bosses and against the walls of the skirt in the region of the bosses at points substantially at right angles to the axis of the wrist pin. These resilient bodies, whether of the first or second type do bring the piston skirt into shape, but because of their inherent resilience cannot support the skirt to resist inward yielding .while it is under the tremendous compression and power impulses.

It is here that the invention is introduced. In most of the forms of the invention (Figs. 1 to 5) it is a supplement to the known resilient bodies of the two types, and of other types of trusses, converting such bodies into practically rigid, nonyielding trusses when the point of maximum exkeep the piston true to the bore pansion has been reached under working conditions of the piston. Having been converted into rigid trusses, the erstwhile resilientbodies hold the skirt in true form with no chance of inward collapse and consequently no chance of any rocking motion being set up to permit the rings to dig into the cylinder walls to set up the very condition which the use of the resilient bodies is intended to prevent.

Referring to the drawing. Figure 1 illustrates a skirt 1 in which an expanding ring 2 of the Phillips type is fitted according to the arrangement disclosed in his patent. The ends-3 of the ring are turned inwardly in parallelism to provide confronting bases. Pads 4 are mounted on the bases. The mounting may be accomplished in any desired manner. One mode of mounting comprises rivets 5.. The near ends of these must be sunk flush or beneath the confronting faces of the pads 4 so that the rivet ends will not produce a false measurement.

There is a space 6 between the confronting faces of the pads. This space has been commonly called a split, especially in the foregoing Bruegger patent. It is metered to a dimension which is previously estimated to be proportionate to the over-expansion of the skirt. This over-expansion must be construed as maximum expansion. In other words, when the skirt is expanded as much as possible, the space 6 must have practically disappeared and the confronting faces of the pads 4 virtually brought into solid abutment.

The skirt 1 has a slot 7. This runs lengthwise of the skirt. Generally this and the other slots (not shown) are much too large. The result is that when the skirt has expanded to the maximum there is still slot room which permits collapse of the skirt under the pressures against the cylinder wall already mentioned. Regardless of the size of the slot 7 the pads 4 will produce an absolute stoppage of skirt collapse, because when the maximum of expansion has been reached'the space 6 will be practically closed and theskirt will be reinforced against collapse because of the solid truss into which the ring 2 is now converted.

Figure 2 shows the ends 3 of the ring 2 more in the form of offset lugs. The offset would be in the direction of the axis of the ring. It is not absolutely essentlalbut the oflset makes the head of a machine screw 8 more easily accessible for adjustment. Its lock nut 9 is also more easily reached. The purpose of adjustment of the screw 8 is to fix the dimension of the metered space 6', the same principle prevailing .here as in Figure 1.

Figure 3 shows the ring 2' as having ends 3 either of the'form in Figure 1 or 2. One or both of the ends (only one in Fig. 3) is used as the base for shims 10. These will be added or subtracted until the metered space 6 is of the proper size.

Figure 4 shows the ring 2 as having endsil'= much on the order of the original form in Figure 1. Instead of being made relatively far apart in the original manufacture as in Figure 1 they are brought so close together that the metered space 6 will be original-in the ring. In some instances a very thin grindstone'will be used to dress the confronting surfaces in order to make the cross dimension of the space 6 exactly what it should be. Figure 4 is intended to show that some of the confronting surfaces of the ends 3 have been ground away so as to bring the space 6 to the proper dimension.

Figure 5 is a section taken higher up across the piston skirt 1. The wrist pin bosses 11 are shown. This view also illustrates the second type of expander. This is a resilient body the sides 12 of which press outwardly against the bosses, and the ends 13, 14 of which press outw'ardly against opposite sides of the skirt in directions at right angles to the axis of the wrist pin.

The end 14 might be said to be double, that is to say, it is turned up in double formation at 3 I in general agreement with the ring arrangement in Figure 1. The useful space between the'ends .3 will be metered according to any of the plans in Figures 1, 2, 3 and 4. The set'screw 8', equivalent to 8 in Figure 2, is merely shown for illustration. The dimension of the space 6 is subject to adjustment. 0

In brief review of what has been stated above, four of the trusses are made with an adjustment. Adjusting means is, therefore, a feature common to Figures 1, 2, 3, and 5. Adjustment is not contemplated in Figure 4. The ring 2 is provided with the metered space 6 of proper size in its original manufacture.

Figure 6 distinguishes mainly from the preceding forms by having the truss 15 cast integrally with the skirt 1. The truss is in the form of a semi-circular bead appearing on the inside of the skirt near. the bottom. 69 is the metered space. The confronting ends of the truss which establish this space may protrude slightly into the over-sized slot '7. The space 6' will virtually close entirely to a solid abutment of the ends. of the truss 15 when the piston has reached its maximum expansion. The slot '7 may not be closed under the same condition, it being possible that this slot remains open perpetually.

Again reviewing what has been stated, it will be recognized that the metered space is identified with a truss or annulus of some sort, either in the form of an inherently separate spring ring as'inFigures 1,2,3 and4, orintheform ofan originally integral .truss as in Figure 6. In any case abutment of the ends of the truss or annulus establishes a solid annular support in 'the skirt of the piston, preventing collapse of the skirt as already brought out.

The making of the space 6 (Fig. 6) involves a special step in the method of casting the piston. The space 6 will be fixed to begin with. Sawing or otherwise kerflng the metered space as contemplated by the Bruegger patent is thus avoided. The method now in mind promotes the rapid production of pistons embodying the principle of the present invention.

Figure 7 illustrates the particular step of the method in mind. 16 is the flask of a mold in which there is a sand or other core 17. The space 18 becomes the piston skirt when filled with molten metal. The slot '7 may be made by inserting fillers 19 of any convenient thickness at the proper place in the skirt line in the process of casting, or by sawing in the usual manner.

This means that the metering shim 20 may stay in the casting during machining and that in order to make the slot 7 either a circular saw or miller is used. When the saw or miller has reached the edge of the metered part the piston may be spread apart and the thin shim removed. No especial care needs be taken to select fillers 19. (or saw) of a determined thickness because no especial care is now taken in making the expansion slots of known pistons.

But especial care is taken in the selection of the shim 20 (Fig. '7). It will be emplaced in line with the groove 21 which later becomes the truss 15 (Fig. 6). The thickness of the shim 20 determines the cross dimension of the space 6 The fillers 19 and shim 20 must. comprise a substance which will not fuse at the temperature of the molten metal. In practice it may .be desirable to make them in one-piece to help in casting. They may be treated so as to permit extraction from the cold casting.

The mode of operation of the truss in any of the various forms of the invention is readily understood. Consider the piston 1 (Fig. 1) as consisting of aluminium alloy. It is known that this piston has a certain inherent expansion. When this piston is first placed into the cylinder there is an initial clearance on all sides, and where the piston starts to heat up it consumes this initial clearance until its outer walls touch the walls of the cylinder.

But there is yet an amount of over-expansion of the piston to be accounted for; It must be borne in mind that in expanding the piston enlarges both radially and circumferentially. It is the radial enlargement that consumes the initial clearance. This subsequent over-expansion occurs circumferentially.

It is then that the slot 7 will become narrower.

- However, it will not close because it is over-sized pleted its over-expansion the pads 4 will be in virtually solid abutment and the spring ring 2 converted into a solid truss which is incapable of inward yielding due to the'pressing in of the skirt.

What has been said with respect to Figure 1 applies to Figures 2 to 6 as well. In every case when the piston skirt reaches itsmaximum expansion it automatically makes for itself a solid annular rib, truss or base, or what is the same thing, it converts an inherently inserted body into a rigid, non-yielding body which fortifles the skirt from the inside against collapse by externally applied collapsing pressures.

I claim: L v

1. In a piston having a slot in its skirt to permit expansion; an annulus situated inthe skirt to fortify it circumannularly as a guard against collapse of the skirt under working conditions due to the presence of the slot, said annulus having a split metered proportionately to the known over-expansion of the skirt so as to cause closure of the split and convert said annulus into a solid truss."

2. In a piston having a slot in its skirt to permit expansion; an annulus situated in the skirt to fortify it circumannularly as a guard against collapse of the skirt under working conditions due to the presence of the slot, said annulus having a split which is open while the skirt is substantially cool but closes approximately at maximum expansion of the skirt under heat and thereby converts said annulus into a solid truss.

3. In a piston having a slot in its skirt to permit expansion; expander means located within the skirt, said means having an inherent resilience exercising outward pressure on the skirt at circumferential points, said means having a split metered proportionately to the known overexpansion of the skirt by heat under maximum working conditions to cause closure of the split and convert said expander means into a virtually solid truss.

4. In a piston having a slot in its skirt to permit expansion and having wrist pin bosses; expander means located in the skirt in the zone of the bosses, said means having inherent resilience exercising outward pressure against the bosses and on the skirt, said means having a split of a size proportioned to the known over-expansion of the skirt by heat under working conditions and adapted to then close and convert said expander means into a solid truss.

5. A piston having a slot in its skirt to permit expansion and a resilient open-ended ring inserted in the skirt; means carried by at least one end of the ring to reduce the size of the opening in the ring, said means being arranged to define a space metered proportionately to the known over-expansion of the skirt under working conditions. 6. Internal expander means for pistons having confronting bases always spaced apart, and means mounted on at least one of the bases to reduce the space to a predetermined size.

7. Internal expander means for pistons having confronting bases always spaced apart, and adjustable means mounted on at least one of the bases to reduce the space to a predetermined size.

8. An internal expansion ring for pistons having opposed bases spaced apart a distance proportioned to the known over-expansion of a piston skirt in which the ring is insertable.

9. In a piston skirt, a bead cast integrally thereof to comprise an annular truss, said bead being split at least at one point, the spacing of said split being proportioned to the over-expansion of the skirt by heat under working conditions.

ZENO ARNO BRUEGGER. 

